1. Field of the Invention
The present invention relates to a synthetic resin pipe which is mainly used in the underground. More particularly, the present invention relates to a synthetic resin pipe, in which an inner surface and an outer surface are flat and smooth, used for leading communication cables or power transmission wires, or used as a water pipe for water and sewerage.
2. Description of the Related Art
Synthetic resin corrugated pipes are conventionally used. In a synthetic resin corrugated pipe, an inner surface is formed flat and smooth and an outer surface includes projecting parts and depression parts alternately in the pipe axis direction to withstand strong pressures from inside or outside.
This type of corrugated pipe has concave portions and convex portions on the outer surface and a resistance for pulling the pipe in is large so that a smooth working process may not be obtained. Further, in order to connect this type of pipes to each other, a particular joint structure is required to fill gaps of the concave portions to keep out water.
For this situation, a synthetic resin pipe is disclosed, in which an outer pipe is composed of a belt-like synthetic resin rolled to bridge convex portions so that the outer surface is approximately flat and smooth (See Japanese Patent Laid-Open Publication No. H8-258177, for example).
According to this type of synthetic resin pipe, the outer surface is formed approximately flat so that the pulling resistance becomes dramatically small and the workability is improved. Further, water-stop performance at a connecting part can be improved compared to the conventional corrugated pipes.